Field of the Invention and Related Art
The present invention relates to an organic solar cell.
An organic solar cell may be composed by forming a p-n junction between silicon, etc. and an organic dye, or by joining a metal and an organic dye so as to convert light energy into electric energy. The organic dye may be a natural dye such as chlorophyll, synthetic dye or pigment such as merocyanine or phthalocyanine, an electroconductive polymer such as polyacetylene, or a composite material of these which may be formed into a film by vacuum evaporation or casting.
An organic solar cell has advantages such as a better economic factor and a lower production cost compared with a conventional solar cell obtained by forming a p-n junction on a single crystal such as silicon, germaium, etc. so that it attracted attention and has been developed in recent years as a solar cell for civil use.
When an organic photoconductive material is used as a solar cell, produced photo-carriers are transported due to a potential difference across a Schottky junction formed between the organic photoconductive layer and a metal electrode to produce photo-electromotive force. A layer comprising an organic photoconductive material, however, involves difficulties in carrier transport characteristics, such as frequent carrier trapping and a low carrier mobility. For this reason, it has been proposed to form a new device form wherein the organic photoconductive layer is functionally separated into a charge generating substance and a charge transporting substance so as to facilitate carrier movement.
However, most charge transporting substances used in such a function separation-type organic solar cell absorb low wavelength light, so that when they are irradiated with light such as sunlight for a long period of time, the charge transporting substances are liable to cause denaturation or degradation, resulting in an increase in carrier trapping or a decrease in mobility which retards carrier movement. Thus, there is involved a problem of lowering in conversion efficiency due to instability against a strong irradiating light.